A conventional brake system for a vehicle frequently has a nonlinear relationship between a driver brake force, which a driver exerts on a brake input element of the brake system, and a braking force, which is applied to a braking component situated on a brake master cylinder. In particular, such a brake system, such as the servobrake device discussed in DE 197 22 739 C2, for example, often has a jump-in range which is perceptible to the driver during the operation of the brake input element.
FIGS. 1A and 1B show two coordinate systems to illustrate an example of a relationship between a driver brake force and a resulting braking force. The abscissas of the coordinate systems show a driver brake distance z, by which an input piston, which is coupled to the operated brake input element, is displaceable. The ordinate of the coordinate system of FIG. 1A shows driver brake force Ff to be applied to displace the input piston by driver brake distance z. In the coordinate system of FIG. 1B, the ordinate specifies resulting braking force Fe.
As is apparent in FIG. 1A, the driver must apply a minimum force Fm to move the input piston, which is in its starting position (z=0) when the brake input element is not operated, out of this position. During subsequent jump-in range J from the starting position up to a driver brake distance zj, driver brake force Ff to be applied to displace the input piston is comparatively low and nearly constant. In jump-in range J, braking force Fe only increases with a small slope. From driver brake distance zj, driver brake force Ff and braking force Fe become increasingly steeper and subsequently merge into an approximately linear range.
Jump-in range J often results from an air gap between the input piston, which is present in its starting position, and a disc (reaction disc), via which the driver brake force is transmittable from the input piston to a braking piston situated on the brake master cylinder after a displacement of the input piston by driver brake distance zj. Since in this case there is no contact for the force transmission between the input piston and the reaction disc in the event of a driver brake distance less than zj, braking force Fe is typically exerted on the braking piston by a brake booster drive in jump-in range J. The brake booster drive is typically activated in such a way that a booster piston, which is situated on the brake booster drive and contacts the disc, is synchronously moved with the input piston in such a way that a nonzero differential distance does not exist between the input piston and the booster piston.